Quench questions

[6667fan]

I have the stroker 427 out of my Fairlane for freshening. The last time it went together the pistons were .015 in the hole. Ended up using some Cometics that had a compressed thickness of .027. The upper rod bearings show signs of detonation, not pounded out of shape but more wear than the bottom shells. Also wear in bores that might be piston rock? The engine was asked to eat some oil smoke the last two years.
Should I look to have the block zero decked and go with a thicker gasket this time? This assumes I will be using the same rotating assembly which is not certain right now.

Thanks

[jayb]

Wear in the bore from piston rock is real common on stroker engines that have seen some miles.  I wouldn't worry too much about that, just get the bores honed and you should be good to go.  Might be a good idea to get the skirts coated if you are seeing that.

Detonation can make the pistons rock more, which will worsen this problem.  As far as the bearing wear goes, a .042" quench distance is about right for optimum quench, which helps prevent detonation.  If you were going to go more to lower the compression ratio, you wouldn't necessarily need to zero deck the pistons.

[6667fan]

Thanks Jay
Not seeking to lower compression, just take prudent steps to avoid detonation scenarios. The compression was 11.3-1. Without adding Ultra Race gas additive the engine would like to run on. ( idle was 800-900, idling off secondaries). Timing almost always at 32 total. Experimented with colder plugs. I mentioned the engine eating oil because that probably did not help the octane rating and could contribute to detonation.
So if the quench number is good, it won’t make any difference from a detonation standpoint if the pistons are .015 down?

[blykins]

Thanks Jay
Not seeking to lower compression, just take prudent steps to avoid detonation scenarios. The compression was 11.3-1. Without adding Ultra Race gas additive the engine would like to run on. ( idle was 800-900, idling off secondaries). Timing almost always at 32 total. Experimented with colder plugs. I mentioned the engine eating oil because that probably did not help the octane rating and could contribute to detonation.
So if the quench number is good, it won’t make any difference from a detonation standpoint if the pistons are .015 down?

Not from my experience.  I've ran pistons down in the hole with a thin gasket and I've ran the pistons sticking way up (about .025") with a thick gasket. 

If you're seeing detonation, you need more octane or less compression. 

[Barry_R]

The quench number is "good enough", and not like the cause of detonation.
Eating oil will definitely contribute to detonation.

Upper rod bearings always have more wear than the lowers.  Are there other signs?
"Chicken tracks" in the upper bearing material?
Were the bearing shells loose - fell out of the rods easily - or were they still snug?
How did the spark plugs look?
Any material chipped out of the sides of the pistons - or the upper ring moly?
Second ring real tight in the groove or normal?

Run on after shut down is not detonation. 
It's not really spark related at all - the ignition is "off".
It's usually excessive closed idle airflow and - counter-intuitively - not enough base timing.

[6667fan]

No chicken tracks in upper bearings, not loose.  I did a quick check of each piston before I brought the parts to builder. I thought I would find a compromised ring land but did not see anything, however that was with rings still on. Rings not snug at all, they are the Mahle 1,1,2 pack. ( GZ  vacuum pump in system, was added later). The rings went in with gaps of top @.018, second @.020.
Is some blow by the norm with those rings?

Base timing 11•. Not equating the run on with detonation, but can always tell when the ratio of additive is too low as run on sets in. Easy enough to add base in and change bushings in distributor. That the idle airflow is too low is also counter intuitive to me, lol.

Thanks much

[blykins]

Wow, that's low initial.  Engine may thank you with that bigger cam to run 16-20. 

[6667fan]

Brent, the engine would fire nice when hot. No vac advance. 32 total by 2400-2500.( most power @32• on dyno.)  Aluminum flywheel, very responsive. As mentioned above I could put more initial in and take some total out via a bushing swap.

If I get to the total I need quickly/cleanly will more initial do more for me besides help with the run on?

Thanks

[My427stang]

Yes more initial will allow you to close the secondaries for the same idle rpm and help run on.

I may have missed it but what were rod clearances and how long has it been running? May not be an issue at all just normal wear

[blykins]

Brent, the engine would fire nice when hot. No vac advance. 32 total by 2400-2500.( most power @32• on dyno.)  Aluminum flywheel, very responsive. As mentioned above I could put more initial in and take some total out via a bushing swap.

If I get to the total I need quickly/cleanly will more initial do more for me besides help with the run on?

Thanks

Yes, I think it would clean your tune up.  More complete combustion on a "dirty" cam. 

[6667fan]

Rod clearances.0025-.0027
Engine last freshened in ‘20. Been asking it to eat oil for 3 seasons. Not lots of miles, but few easy ones.

I would say 92• of overlap qualifies as dirty.😝

Thanks

[blykins]

Yeah, I’ve learned a lot since then.  Certainly not what I would go with today.

[6667fan]

There is evolution all around my friend. Before it was “well, it’s gonna see a little time at the track” to, “ well, it’s a strip/street car now and let’s try to get a number” 😆